In recent years, full color image formation has been practically used in the image formation method of the electrophotography system using an electrostatic charge image development (hereafter, it is called as an electrophotographic toner, or simply called as a toner). Specifically a full color image is formed as follows: the electrostatic latent image corresponding to a manuscript pattern (picture information of a manuscript) is formed by exposing the light separated into spectrum components on a photo conductor; this electrostatic latent image is developed using each color toner, and a plurality of monochromatic toner images is superimposed to form a full color image. The color toners which form a color image are, for example, a yellow toner, a magenta toner and a cyan toner. They containing a binder resin composed of a thermoplastic resin, and a colorant of each color.
Moreover, in recent years, a full color image forming apparatus of an electrophotography system has come to be used by progress of a digital technology, also in the field of small volume printing. That is, full color print production by an electrophotography system has become used to a large extent in the field of small volume printing. In the field of small volume printing, there are many print order opportunities of small-quantity number of sheets. The electrophotography system has an ability of the printing the required number of sheets to be created on demand base, without producing a printing plate which is usually made in conventional printing field (for example, refer to Patent Document 1).
As a colorant which constitutes a color toner, a well-known organic pigment and oil-soluble color can be mentioned conventionally. Heretofore, either an organic pigment or an oil-soluble color has been chosen, or these were mixed and the color toner has been designed.
For a full color image formation, it is required to visually recognize the undermost bottom color on which other colors are superimposed, without being shielded by other colors covered to the bottom color.
The expected toner is to have a sufficient transparency after the color image is fixed. Although the organic pigment is generally excellent in a heat-resisting property or light resistance compared with the oil colors since it exists in the state of dispersion of a grain shape in the toner, the shielding power of the toner will become strong and it has a defect in which the transparency of a toner is reduced. Moreover, since good dispersibility of a pigment is generally hard to acquired, transparency of the toner became still smaller. The pigment has a problem of reducing color saturation of the formed image and good color reproduction is hard to be obtained.
Therefore, in order to visually recognize correctly the undermost bottom color on which other colors are superimposed, without being concealed by the upper colors, the colorant composed of the toner is required to have a good dispersibility and a stable color reproduction property. In producing a full color prints, such as a catalog and an advertisement, with a toner, the employed toner for them is especially required to exhibit faithful color reproduction of the original. That is, in performing full color image formation, when a yellow, magenta, and cyan toner image each are superimposed to a targeted color image, color toners having a good color reproduction property are demanded.
And examination of various colorants has so far been made for the purpose of improving a color reproduction of a color toner. For example, one of the typical magenta colorants for color toners is a quinacridone pigment. Since it has a good magenta color tone and outstanding light resistance, the toner using a quinacridone pigment is used for general-purpose.
However, a quinacridone pigment has a problem in the dispersibility (during toner formation, quinacridone pigments tend to be coagulated and localized in micro-scale) in the inside of a toner, and is easy to generate impure color at the time of a color pile. Therefore, it was difficult to reproduce faithfully the picture on the computer graphics which is high, or a high saturation display picture, which is highly demanded in recent years. Then, an examination to use an additional dye with a quinacridone pigment was carried out aiming at improvement in color saturation (for example, refer to Patent Document 1). Moreover, a technology of having used other pigments together with a quinacridone pigment and performing a toner design was investigated. An example is to use a naphthol pigment with a quinacridone pigment (for example, refer to Patent Document 2). And other example is to use an anthraquinone pigment with a quinacridone pigment (for example, refer to Patent Document 3).
However, each combination which uses these colors and other magenta pigments was inferior in light resistance compared with the case using a quinacridone pigment independently. And when the combination system was used over the long period of time, it had a problem which cannot maintain a stabile color.
Furthermore, the technology of manufacturing a toner by the polymerizing method using the colorant which is composed of a metal compound and a coloring matter as a means to realize image formation of high color saturation also came to be proposed (for example, refer to Patent Documents 4). However, the toner indicated in Patent Documents 4 had a problem of offset property at low temperature at the time of fixing to result in producing a blot at fixing, in spite of having an outstanding hue region and transparency. Therefore, it was difficult for it to perform stable print production over a long period of time.
Patent Document 1: Unexamined Japanese patent application publication (hereafter it is called as JP-A) 2007-286148
Patent Document 1: JP-A 2006-267741
Patent Document 1: JP-A 2006-154363
Patent Document 1: JP-A 2007-316591